尝试访问文档字段时 Flutter/Firebase 中的额外位置参数

Question

I'm trying to print a specific users info from firebase, but whenever I try to call the specific value, such as name, it always comes up as the error, Too many positional arguments: 0 expected, but 1 found.

getUserState() async{
  String temp;
  final FirebaseAuth auth = FirebaseAuth.instance;   
  final String id = FirebaseFirestore.instance.collection('users').id;
  FirebaseFirestore.instance.collection('users').doc(id).get().then((value){
    temp = value.data('name') as String;
    
  });

Answer 1

data is a method that takes no parameter and returns a Map

Try this:

    temp = value.data()!['name'] as String;

Answer 2

To print an specific user information from Firebase calling by a value such as name, you can use the Firebase Database Query API. You can use the orderByChild() method to query the database and retrieve data based on a specific value. For example, if you want to print an user information from Firebase calling by name, you can use the following code:

    // Get a reference to the database
    var database = firebase.database();
    
    // Query the database for user information based on name
    var query = database.ref("users").orderByChild("name").equalTo("John Doe");
    
    // Get the user information from the query
    query.once("value", function(snapshot) {
      var userInfo = snapshot.val();
    
      // Print the user information
      console.log(userInfo);
    });

Answer 3

You can use .get to read map

 temp = value.get('name') as String? ?? "" ;

Answer 4

If you need a function that returns a String that contains the name you can refactor your code like the following:

  Future<String?> getUserState(String userId) async {
    final docRef = await FirebaseFirestore.instance.collection('users').doc(userId).get();
    final user = docRef.data();
    return user?['name'];
  }

user : is a Map<String, dynamic> representation of your document in collection. You can use it to covert in your model with fromJson for example.

If any users found with provided id it returns null